Apparatus for treating thermoplastic synthetic plastics material

ABSTRACT

An apparatus for pre-treatment of thermoplastic synthetic plastics material, for example polyester waste, comprises at least two receptacles (1,13) disposed in series following each other, in each one of which receptacles a comminuting or mixing tool (5) rotates around a vertical axis (4) in the bottom region of the receptacle (1 or 13). At least the downstream receptacle has an evacuation line (18) through which, optionally also a protective gas can be introduced. The receptacles (1,13) are connected to each other by a tube piece (12) in which a shut-off means (20) is disposed so that the vacuum in the downstream receptacle (13) can be maintained without any problem until the shut-off valve (20) is opened, whereupon the vacuum in the receptacle (13) sucks on the material positioned in the upstream receptacle (1). Therefore, in the upstream receptacle (1)--when seen in flowing direction of the synthetic plastics material--the synthetic plastics material is pre-comminuted, pre-heated, pre-dried and pre-compressed, what is still assisted by the turbulence when sucked-in into the downstream receptacle (13). In such a manner, completely homogeneous material is conveyed by a worm (16) connected to the last receptacle (13) to further processing (FIG. 1).

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an apparatus for treating thermoplasticsynthetic plastics material, for example waste, in particular ofpolyester, comprising a receptacle for material to be treated to whichthis material is supplied through an intake opening and from which thematerial is delivered by at least one worm connected to the sidewall ofthe receptacle, at least one tool having working edges actingcomminuting and, respectively, or mixing on the material disposed in thebottom region of the receptacle and being rotatable around a verticalaxis, the intake opening of the worm being disposed at leastsubstantially at the level of the tool, and at least one line connectedto the receptacle for creating a vacuum within the interior of thereceptacle and, if desired, for supplying a gas therein.

Such apparatus are known (EP-A 390,873), and generally they worksatisfying, also when treating such kinds of synthetic plastics materialwhich are sensitive to air oxygen and, respectively, or humidity,because by evacuating the receptacle or by supplying a protective gasinto the interior of the receptacle, the synthetic plastics material canbe protected against these detrimental influences.

However, it has been shown that in some cases the degree of homogenizingof the synthetic plastics material delivered by the worm is notsufficient, in particular with respect to the obtained drying degree ofsuch synthetic plastics material which must be completely dry alreadybefore plasticizing in order to avoid downgrading, for examplepolyester. Polyester elements, for example foils of greater thickness,require an increased effort in drying which increases with the thicknessso that for such material separate drying processes, for example withdehydrated air in special drying apparatus are required. Further, thesedrying apparatus operate in a temperature region that is admissible forcrystalized material only, however, amorphous material would get stickyso that it would agglomerate. This means that a crystallizing processmust antecede the drying process. However, if the material to be treatedis treated for a long time in the receptacle, then at a continuousoperation of the apparatus there occurs the danger that single syntheticplastics material elements are already clutched by the delivery wormalready at a very early moment, however other synthetic plasticsmaterial elements only at a very late time. Those synthetic plasticsmaterial elements which were taken along early, may still becomparatively cold and, therefore, not pre-treated to a sufficientamount, so that the said inhomogenities in the material occur that issupplied by the worm to the connected tool, for example to an extruderhead.

The invention has at its object to avoid these disadvantages and tosubstantially improve the homogenity of the delivered material, by usingthe vacuum effect within the receptacle in an advantageous manner. Theinvention solves this task by the features that the delivery opening ofat least one further receptacle is connected to the intake opening bymeans of a tube element, in which receptacle also at least one toolrotating around a vertical axis is disposed in the bottom region of thereceptacle, and that in the tube element a shut-off means forpressure-tight closing of the tube element is disposed for maintainingthe vacuum within the interior of the receptacle provided with the line.Therefore, within the inventive apparatus two or more receptacles aredisposed in a series and the synthetic plastics material to be treatedmust run through these receptacles one after the other. Within the firstreceptacle, already a pre-treatment of the synthetic plastics materialtakes place by a pre-comminuting, pre-heating, pre-drying andpre-compression, so that pre-homogenized material is created which issupplied to the following receptacle. Thereby it is ensured that nountreated (cold, not compressed, not comminuted or inhomogeneous)material is directly supplied to the delivery worm and via this to theconnected extruder or the like. By means of the shut-off means withinthe tube element connecting the receptacles, a complete and reliabletightening between the two receptacles can be obtained so that losses inthe vacuum or in the protective gas within the following receptacle arecompletely avoided as long as the shut-off means remains closed, thatis, as long as the pre-treatment takes place within the precedingreceptacle. Therefore, the advantages of the pre-treatment can bemaintained also if within the second or within a following receptacle avacuum treatment or protective gas treatment of the thermo-plasticsynthetic material takes place. The vacuum of this treatment is evenused for an increase of the mixing effect and, therefore, for improvingthe homogenity of the material delivered from the downstream disposedreceptacle, because, when the shut-off means is opened, the vacuumwithin the downstream receptacle suddenly sucks on the material disposedwithin the upstream receptacle so that an abrupt mixing takes placewithin the downstream receptacle by vacuum influence.

Particularly favourable results are obtained if according to a furtherembodiment of the invention the exit opening of the further receptacle(that is the upstream receptacle) is disposed at least substantially atthe level of the tool within this receptacle, that is within the bottomregion of the receptacle, because then the said sucking-off of thematerial disposed within the upstream receptacle can take place withouta substantial deviation thereof. Further, if the shut-off valve isopened when the tool still rotates, the tool rotating within theupstream receptacle delivers by centrifugal action into the exit openingso that the material pre-treated within the upstream receptacle isconveyed into the downstream receptacle within the shortest possibletime. As soon as the shut-off valve is closed again, a fresh batch canbe introduced into the upstream receptacle and can be pre-treated there.

Within the EP-A 496,090, which has a better priority, however is notpre-published, is has been proposed to mount two receptacles providedwith rotating comminuting tools for the treatment of synthetic plasticswaste material in a series. The material is introduced into the secondreceptacle by means of a conveyor worm from the first receptacle.However, such a conveyor worm cannot be made pressure-tight.

Within the spirit of the invention, in the simpliest case the shut-offmeans may comprise a gate plate which is closed as soon as the vacuumtreatment or the gasification takes place within the downstreamreceptacle. However, then no continuous operation is still possible, tothe contrary, the downstream receptacle must be charged batchwise. If,however, according to another embodiment of the invention the shut-offmeans is a sluice, in particular a cellular wheel sluice, the saidtightening between the two receptacles is maintained and nevertheless acontinuous operation is possible. In order to avoid that too greatvacuum losses occur through the cells of the sluice, these cells canalso be evacuated or a gas can be introduced therein.

As already mentioned, the vacuum created within the downstreamreceptacle enhances sucking-in of the material to be treated from theupstream receptacle. Within such plants, therefore, the receptacles as arule can be disposed at the same level. However, if it is desired toimprove filling of the downstream receptacle or mixing the materialtherein by influence of gravity, according to a further embodiment ofthe invention the receptacle disposed upstream, when seen in flowingdirection of the material, may be disposed at a higher level than thefollowing receptacle. The latter, therefore, can also be charged withinits middle section or in its upper section of its sidewall, andoptionally also through the cover from above.

Within the spirit of the invention, it has been shown that it isparticularly favourable to provide the exit opening of the, when seen inflowing direction of the material, upstream receptacle with anenlargement at the arriving side of the tool. This enlargement ensuresthat the material can better flow into the flow cross section. Accordingto the invention, an analogous improvement is obtained at the exit sideof the transition cross section, if the intake opening of the, when seenin flowing direction of the material, downstream receptacle has anenlargement at that side at which the tool runs off. Within the spiritof the invention, the enlargements may be of pocket-like configuration,preferably having a sickle-shaped cross section, in order to ensure asmooth introduction or delivery of the material into the receptacle orout of it. dr

BRIEF DESCRIPTION OF THE DRAWING FIGURES

In the drawing, exemplative embodiments of the invention areschematically shown. FIGS. 1, 2 and 3 each show a vertical sectionthrough different embodiments of the invention. FIG. 4 is a horizontalsection showing the configuration of the pocket-shaped enlargements ofthe transition cross section. FIG. 5 is a section taken along the lineV--V of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Within the embodiment according to FIG. 1 a first receptacle 1 isprovided to which the thermoplastic synthetic plastics material to betreated, for example waste polyester in form of foil remnants, usedarticles (for example bottles) and the like is continuously suppliedthrough an intake opening 2 by means of a conveyor 3. A tool 5 rotatablearound a vertical axis 4 is disposed in the bottom region of thereceptacle 1 and is driven for rotation by a motor 6 and comminutes andmixes the synthetic plastics material within the receptacle 1. For this,the tool 5 comprises at least two arms which extend perpendicularly tothe axis 4 and are provided with working edges 7 acting on the syntheticplastics material. When seen in rotation direction (arrow 8, FIG. 4) ofthe tool 5, these working edges 7 are angle-bent so that, on the onehand, they exert a drawing cut on the synthetic plastics materialdisposed in the marginal area of the receptacle 1 and, on the otherhand, convey the comminuted material like a spatula into a deliveryopening 10 disposed in the sidewall 9 of the receptacle, which openingis substantially disposed at the same level as the tool 5. The syntheticplastics material rotating within the receptacle 1 arises along thesidewalls 9 of the receptacle 1 and forms a mixing trombe, the shape ofwhich depends from the kind, the quantity and the velocity of thematerial. A two-part tube element 12 comprising a shut-off member 20 isconnected to the discharge opening 10, through which tube element thepre-comminuted material expelled from the receptacle 1 reaches a furtherreceptacle 13, provided that the shut-off means 20 is opened, whichfurther receptacle is disposed at the same level as the receptacle 1 andin which further receptacle a tool 5 driven by a motor 8 for rotation isdisposed which is constructed in the same manner as the tool of thereceptacle 1 and is disposed at the same level as the intake opening 14formed by the mouth of the tube element 12. The pre-comminuted materialintroduced through this opening 15 into the receptacle 13 is taken alongby the rotating tool 5 and forms also a mixing trombe 11 in thereceptacle 13. Hereby the synthetic plastics material is furthercomminuted and homogenized and lastly is conveyed by the tool 5 in theintake opening 15 of a worm. 16, the housing 17 thereof suitably isdisposed at least substantially radially with respect to the axis of thereceptacle 13. Suitably, the housing 17 is funnel-like enlarged in thearea of the intake opening 15, in order to facilitate the introductionof the material. The intake opening 15 is disposed at leastsubstantially at the level of the tool 5. The worm 16 conveys thetreated synthetic plastics material to a plant (not shown) connected tothe apparatus, for example to a worm extruder, or the worm 16 mayconstitute the worm of this worm extruder.

For the treatment of such synthetic plastics material which in heatedcondition is sensitive to air access or in order to reduce the dryingtime, a line 18 opens into the receptacle 13 and is connected to a means19 for creating a vacuum within the receptacle 13 or, respectively, forintroduction of a protective gas into this receptacle 13. Maintenance ofthe desired atmosphere or of the desired pressure within the receptacle13 is ensured by the shut-off member 20 mounted in the tube element 12,what is facilitated by a two-part construction of the tube element 12.In the exemplative embodiment shown, this shut-off means 20 is formed bya gate plate 21 connected to the piston rod of a pressurized cylinder22. This gate 21 tightens the receptacle 13 completely with respect tothe receptacle 1.

The embodiment according to FIG. 2 differs from that according to FIG. 1mainly in that a third receptacle 23 is provided upstream the receptacle1 and the discharge opening 10 of which is connected to the intakeopening 14 of the receptacle 1. Comminuting, heating, drying andcompression of the treated synthetic plastics material for the purposeof its homogenisation is made in three steps here. Lines 18 are againconducted into the last two receptacles 1,13 for evacuation of thereceptacles or introducing gases into them. The first two receptacles23,1, when seen in flowing direction of the material, may again beconnected by means of a tube element 12 in which, as this is shown inFIG. 1, a shut-off means 20 formed by a gate valve may be inserted, asthis is also shown in FIG. 2 for the tube piece 12 connecting the tworeceptacles 1,13. Since the shut-off by means of a shut-off device inform of a gate valve does not enable a completely continuous operation,the shut-off means 20 in the tube piece 12 between the receptacle 23,1is constructed in form of a cellular wheel sluice 24, the cellular wheelof which rotates in direction of the arrow 25. Such a cellular wheelsluice may also replace the gate valve disposed between the receptacles1,13. When seen in direction of rotation (arrow 25) of the cellularwheel, the cell of the cellular wheel 24 preceding the discharge opening10 is connected by means of a line 26 to the apparatus 19 for evacuationor gas-introduction, so that, therefore, the pre-comminuted materialdischarged from the receptacle 23 can be already evacuated or broughtinto contact with a protective gas, before it is introduced into thereceptacle 1. A further line 27 may be conducted to the cells disposedin front of the discharge opening 10, when seen in rotation direction ofthe arrow 25, for the purpose of evacuation of these cells and therebyto enhance sucking-on of the synthetic plastics material from thereceptacle 23.

Whereas within the embodiment described heretofore the receptacles ortheir discharge openings and intake openings are always disposed atleast substantially at the same level and the conveyance of thesynthetic plastics material from the one receptacle into the followingreceptacle is effected by this centrifugal force exerted from the tool5, assisted by the vacuum in the next following receptacle or in thecellular wheel sluice, shows FIG. 3 an embodiment in which tworeceptacles 1,13 are disposed at different levels, the receptacle 13being disposed at a lower level than the receptacle 1. Since the tubepiece 12 is disposed horizontally, the intake opening 14 of thereceptacle 13 is brought into the middle section of the side wall 9.This has as a consequence that the transport and mixing of the syntheticplastics material from the receptacle 1 into the receptacle 13 isassisted by gravity action. This can be increased by inclining the tubepiece 12 towards the receptacle 13.

In FIGS. 4 and 5, the area of the shut-off means 20 is shown in anenlarged scale. FIG. 4 shows that the discharge opening 10 of thereceptacle 1 has an enlargement 28 at the arriving side of the tool 5,which is formed as a pocket having a sickle-shaped cross section (seenin top view, FIG. 4). The intake opening 14 of the following receptacle13 comprises an analogous enlargement 29, however, this enlargement 29is disposed at the leaving side of the tool 5. The two enlargements28,29, therefore, are disposed opposite each other--if desiredmirror-inverted,--as long as the two tools 5 rotate in the samedirection in the receptacles 1,13 what must not necessarily be so. Thesepocket-like enlargements enhance the inflow behaviour or outflowbehaviour of the material streaming in direction of the arrows 13, sothat the streaming resistance through the tube piece 12 is decreased. Ofcourse, also here a sluice, for example in form of the cellular wheelsluice 24, may be used instead of the gate valve for the shut-off means20.

In order to avoid blocking in the tube piece 12, the distance T (FIG. 5)at which the gate plate 21 is spaced apart from the wall 9 of thepreceding receptacle, should be small. It has been shown as suitable todispose the gate plate 21 at the location at which the pocket-likeenlargement 22 shows its greatest depth. Therefore, the gate plate 21generally is disposed excentrically with respect to the center betweenthe two receptacles 1,13.

The embodiment according to FIG. 2 enables it to maintain differentoperation conditions in the two receptacles 1,13 via the lines 18, forexample a vacuum in the receptacle 1 and introduction of a protectivegas in the receptacle 13, or vice versa. However, it is of course alsopossible to maintain a vacuum in both receptacles 1,13, however withdifferent degrees of evacuation, and in doing so, generally the vacuumin the downstream receptacle 13 is adjusted at a greater value than inthe upstream receptacle 1. In such a case, namely, the treated materialis sucked-in into the downstream receptacle, when the shut-off means 20is opened. This holds also if the shut-off means 20 is formed as acellular wheel sluice 24, however, within a cellular wheel sluice 24 theintroduction of the material into the downstream receptacle does nottake place so suddenly as if a shut-off means 20 is opened which isformed as a gate valve.

It would be also possible to connect more than one downstream receptacle13 to a common upstream receptacle 1, for the purpose of increasing thecapacity of the plant. If this is desired, different operationconditions can be maintained via the line 28 in the downstreamreceptacles 13.

In addition, the jacket of each receptacle can be heated or cooled, forexample by means of heating coils or cooling coils or by means of adouble jacket, By this, also different temperature conditions can bemaintained in the individual receptacles.

Further, it would be possible to connect more than one discharge worm 16to one or more of the downstream receptacles 13, and to feed more thanone extruder plant from the receptacle 13.

Further, it would be possible to dispose in some or all of thereceptacles more than one rotating tool 5, for example two toolsdisposed adjacent each other.

What is claimed is:
 1. Apparatus for treating thermoplastic syntheticplastic material comprising:a first receptacle having an intake openingin an upper region thereof and an outlet opening in a lower regionthereof; conveyor means for conveying material into the intake openingof the first receptacle; a second receptacle having an intake openingand an outlet opening in a lower region of a sidewall thereof; a mixingtool mounted in said second receptacle for mixing the material in thesecond receptacle; a tube member connecting the outlet opening of thefirst receptacle to the intake opening of the second receptacle, saidtube guiding material discharged from the first receptacle into thesecond receptacle; means disposed in said tube member for creating anair tight closure between said first receptacle and said secondreceptacle, said means comprising a gate movable in said tube memberbetween a first closed position and a second open position means formoving the gate between said open and closed positions; a worm housinghaving an inlet opening connected to the outlet opening of the secondreceptacle; a worm disposed in the worm housing for conveying materialout of the second receptacle; a gas line connected to the secondreceptacle; and a pump connected to said gas line for moving gas throughsaid gas line, said pump being cooperative with said gate forcontrolling an atmosphere inside said second receptacle.
 2. Theapparatus of claim 1 wherein the first receptacle is positioned at ahigher elevation than the second receptacle.
 3. The apparatus of claim 1wherein the first receptacle and the second receptacle are positioned atthe same elevation.
 4. The apparatus of claim 1 wherein said outletopening of said first receptacle includes an enlargement.
 5. Theapparatus of claim 4 wherein said enlargement is sickle shaped.
 6. Theapparatus of claim 4 wherein said gate is disposed adjacent to theoutlet opening near the bottom of the enlargement.
 7. The apparatus ofclaim 1 wherein said intake opening of said second receptacle includesand enlargement.
 8. The apparatus of claim 7 wherein said enlargement issickle shaped.
 9. The apparatus of claim 1 wherein said first and secondreceptacles can be heated and cooled independently of each other. 10.The apparatus of claim 1 wherein said second receptacle has a verticalaxis and said mixing tool is rotatably mounted in said second receptaclefor rotation about said vertical axis, said mixing tool being furtheroperative for comminuting said material in said second receptacle. 11.Apparatus for treating thermoplastic synthetic plastic materialcomprising:a first receptacle having an intake opening in an upperregion thereof and an outlet opening in a lower region thereof; conveyormeans for conveying material into the intake opening of the firstreceptacle; a second receptacle having an intake opening and an outletopening; a mixing tool mounted in the second receptacle for mixingmaterial in the second receptacle; a first tube member connecting theoutlet opening of the first receptacle to the intake opening of thesecond receptacle; means disposed in said first tube member for creatingan air tight closure between said first receptacle and said secondreceptacle; a third receptacle having an intake opening and an outletopening in a lower region of a sidewall thereof; a mixing tool mountedin said third receptacle for mixing the material in the thirdreceptacle; a second tube member connecting the outlet opening of thesecond receptacle to the intake opening of the third receptacle, saidtube guiding material discharged from the second receptacle into thethird receptacle; means disposed in said second tube member for creatingan air tight closure between said second receptacle and said thirdreceptacle, said means comprising a gate movable in the second tubemember between a first closed position and a second open position; meansfor moving the gate between said open and closed positions; a wormhousing having an inlet opening connected to the outlet opening of thethird receptacle; a worm disposed in the worm housing for conveyingmaterial out of the third receptacle; a first gas line connected to thesecond receptacle; a second gas line connected to said third receptacle;and a pump connected to said first and second gas lines for moving gasthrough said gas lines, said pump being cooperative with said closuremeans in said first tube member and said gate in said second tube memberfor independently controlling atmospheres inside said second and thirdreceptacles.
 12. The apparatus of claim 11 wherein the second receptacleis positioned at a higher elevation than the third receptacle.
 13. Theapparatus of claim 11 wherein the first, second and third receptaclesare positioned at the same elevation.
 14. The apparatus of claim 11wherein said outlet opening of said second receptacle includes anenlargement.
 15. The apparatus of claim 14 wherein said enlargement issickle shaped.
 16. The apparatus of claim 14 wherein said gate isdisposed adjacent to the outlet opening near the bottom of theenlargement.
 17. The apparatus of claim 11 wherein said intake openingof said third receptacle includes and enlargement.
 18. The apparatus ofclaim 17 wherein said enlargement is sickle shaped.
 19. The apparatus ofclaim 11 wherein said second and third receptacles can be heated andcooled independently of each other.
 20. The apparatus of claim 11wherein said second and third receptacles have a vertical axis and saidrespective mixing tools are rotatably mounted in said second and thirdreceptacles for rotation about said vertical axes, said mixing toolsbeing further operative for comminuting said material in said second andthird receptacles.